Gun size significantly impacts the resolving capabilities of a set. You cannot resolve 1080 with anything less than 9in guns without scanline overlap, and a matching loss of sharpness.
I've read a review of the 9" gun Mitsubishi and the results were less than impressive. They are short necked 9" CRTs so they can fit inside the box (otherwise the regular sized 9" guns are way too big) and so the reviewer (I believe it was in The Perfect Vision) compared them to other high end 7" CRT RPTVs like the Sony, Pioneer Elite, and Hitachi and felt the 9" gun really gave you no better picture quality, and somewhat worse than the best 7" gunned RPTV's.
If you want the real benefits of 9" guns, then get a high end CRT front projector. However, they cost a bundle.